From the aspects of energy saving and efficient coating steps, there is a need for coating compositions which are low-temperature curable and highly resistant to chemicals. Among others, compositions comprising a modified acrylic resin and a crosslinker are generally used because of ease of resin production, weather resistance, chemical resistance, and coating strength. Specifically, there are known compositions comprising a hydroxyalkyl-containing acrylic resin and an isocyanate crosslinker and compositions comprising a hydrolyzable silyl-containing acrylic resin wherein the resin is crosslinked via hydrolytic condensation. They are widely used at present.
However, the former has the drawbacks that isocyanate is unstable and difficult to handle, for example, skin irritative. In addition, the isocyanate manufacturing process is quite dangerous because phosgene gas is used. Therefore, the trend is toward the latter approach. For example, JP-A S57-36109 and JP-A S58-15566 propose copolymers of a radically polymerizable monomer and 3-(meth)acryloxypropyltrimethoxysilane. These copolymers have better weather resistance than the acrylic resins of isocyanate crosslinking type. However, most copolymers which are widely used at present contain 3-(meth)acryloxypropyltrimethoxysilane in a molar ratio of less than 5%. Because of fewer siloxane bonds, these copolymers have similar properties to the acrylic resins. Undesirably, coatings of these copolymers tend to have a low hardness and have poor adhesion as demonstrated by a cohesive failure in the adhesion test.